A flexible flowline is comprised typically of several distinct concentric layers that afford strength and flexibility to the flowline. The innermost layer, known as the carcass, prevents collapse of the flowline due to external hydrostatic pressure. The immediately adjacent layer, known as the barrier, is constructed from a synthetic polymer material and serves to prevent content leakage from the flowline. There may also be succession of other layers of varying materials forming the overall composite of the flowline.
A flexible flowline may be utilized, for example, as a dynamic riser to couple a rigid flowline or another flexible flowline on the seabed to a floating vessel or buoy to convey production fluids such as oil, gas or oil/gas mixtures under pressure from an oil/gas well or platform to the vessel or buoy. Hence, an end fitting can be utilized to couple the flexible flowline at each end to an adjacent flowline or wellhead and the vessel or buoy.
A leak-tight seal contained in the end fitting has been achieved in the manner of the prior art utilizing an inner seal ring which encircles and engages the external surface of the flowline barrier. This ring can also hold the barrier and carcass in position within the end by a frictional force generated from the pressure of the seal ring on the barrier layer.
While functioning well, a problem has been recognized that when installing the pipe to within the fitting, the installation has typically required on the order of 30,000-35,000 pounds of force in order to assure the intended fit to both maintain a seal against leakage while preventing pullout from forces likely to be encountered. Such pullout forces can, example be generated from repeated thermo cycling to which the installation is ultimately exposed.
Various forms of couplers and/or end fittings are disclosed in U.S. Pat. Nos. 1,817,776; 2,264,480; 2,341,164; 2,444,380; 3,995,897 and 4,773,680.
Despite recognition of the foregoing, it has not been known heretofore how to satisfactorily eliminate the extremely high loading force incurred during installation of the pipe to within the end fitting.